According to a study published in the Lancet Diabetes, people who have slightly elevated blood sugar that’s not high enough for a diabetes diagnosis may still have a higher risk of heart and kidney disease than individuals with normal blood sugar

Diabetes has long been linked to an increased risk of heart disease. Plenty of previous research also ties diabetes to an increased risk of kidney disease.

Research has been mixed; however, on whether slightly elevated blood sugar that is sometimes called ‘pre-diabetes’ might also increase the risk of heart and kidney issues. Even the name ‘pre-diabetes’ is controversial, and doctors disagree on how to diagnose and treat people with only mildly abnormal blood sugar.

For the study, published in The Lancet Diabetes and Endocrinology, researchers examined a nationally representative sample of 27,971 adults surveyed in four waves from 1988 to 1994, 1999 to 2004, 2005 to 2010 and 2011 to 2014.

By the broadest definition of pre-diabetes, researchers estimated the number of adults with pre-diabetes increased from 56.2 million at the start of the study period to 78.5 million by the end.

For the study, prediabetes was defined as a fasting blood glucose level of 100 to 125 mg/dL or a haemoglobin A1c level of 5.7% to 6.4%.

By the end of the study, many people with pre-diabetes had risk factors for heart and kidney problems: 37% had high blood pressure, 51% had high cholesterol, 24% smoked, 5% had reduced blood filtration by the kidneys, and 8% had elevated levels of the protein albumin in the urine that suggest impaired kidney function.

“Pre-diabetes is extremely common,” said lead study author Dr Mohammed Ali, a researcher at Emory University and for the U.S. Centers for Disease Control and Prevention in Atlanta.

While the study wasn’t a controlled experiment designed to prove whether or how reducing slightly elevated blood sugar might reduce the risk of heart or kidney problems, lifestyle changes like increased exercise and a healthier diet might help people reduce blood sugar and their risk of health problems that can accompany diabetes, Ali said by email.

“Patients who are told they have pre-diabetes should work with their providers to actively address it and initiate sustainable lifestyle changes and/or medications,” Ali advised.

The results offer fresh evidence of the health risks associated with pre-diabetes, said Mika Kivimaki, a researcher at University College London in the U.K. who wasn’t involved in the study. However, the evidence is stronger for the connection with kidney disease than heart disease.

But people with slightly elevated blood sugar should still take steps to get it down to a healthy level.

“I believe people with elevated blood sugar would benefit from adopting a healthy lifestyle and keeping blood pressure and cholesterol at healthy levels because all these have several favourable effects, including a reduced risk of diabetes, cardiovascular disease and kidney problems,” Kivimaki added.